Numerical Simulation of Superplastic Forming of a Magnesium Alloy Part

Abstract:

Article Preview

A numerical simulation of superplastic backward extrusion of a magnesium alloy part is
presented in this paper. In fact, the simulated superplastic forming is not a pure superplastic forming
because of the billet with coarse cylindrical grains. The forming may become a pure superplastic
forming only after dynamic recrystallization and grain refinement appear and the grain boundary
sliding has been the main deformation mechanism. In order to simulate the special forming process, a
constitutive relation considering dynamic recrystallization and the multiform deform mechanism and
the parameter identification of the constitutive relattion are studied. The program for simulation is
able to predict the grain refinement and the transform between different deformation mechanisms.
Finally the calculated results on the grain size and dynamic rerystallization are presented. A
comparison between the calculated and the experimental results shows there is a good agreement
between calculated results and experimental results.

Abstract: A Kumar-type constitutive relationship of TA15 alloy was investigated by non-linear regression analysis, and the equations were established based on test data from hot process simulator. Applying this constitutive equation in commercial FEM software of SFTC/Deform, the hammer forging process of TA15 alloy beam was simulated, meanwhile the final shape of forging piece, the hammering times, the height reduction variation and the maximal effective stress variation along with forging time were predicted. The hammer forging test was carried out and the test results showed that the simulation based on Kumar-type constitutive relationship meet the practical need to a great extent.

Abstract: The hot compressive deformation behavior of the superalloy was investigated at the temperature range from 1050 to 1140 and strain rate range from 0.01 to 10s-1 on Gleeble-1500 thermal simulator. Utilizing hyperbolic sine function and introducing the strain with 4th order polynomial fitting, the constitutive equations of flow stress of spray-forming FGH95 superalloy at high temperature were established. The results show that during the hot compression deformation of the superalloy, the characteristics of dynamic softening were observed, and flow stresses decrease with increasing temperature and decreasing strain rate. The flow stress of the superalloy predicted by the proposed models with 4th order polynomial fit agree with the experimental value well, and the average relative error is 3.64%.

Abstract: This paper describes a new approach for identification of the optimum pressure history for SPF processes, based on mechanisms-based hyperbolic constitutive equations. This equation set has been modified to incorporate the effect of the damage behaviour the material suffers due to the cavitational evolution of Al-5083 superplastic alloy. A large deformation, multiaxial formulation of the constitutive equation set is implemented and applied to finite element modelling of a bulge test forming process to characterise the cavitation evolution behaviour in the bulge test, using conventional (constant strain rate) and the newly proposed (variable strain rate) strategy.

Abstract: Thermo-mechanical experiments were carried out to study the effect of deformation speed and temperature on the behaviour of a non-quenched and tempered steel during hot forging. And an effective method for correction of friction was used to amend the tested flow stress, Meanwhile, the constitutive equations of flow stress-strain for TL1438 steel during hot forming was established based on the amended flow stress and hyperbolic sine which includes Zener-Hollomon parameter, and related parameters of TL1438 during hot forming was obtained by analyzing the data.